It was quite nice, and it'll be good to see the full feature. As Robcbh said, it does seem like just a bunch of kids from the same building, but I see that as a positive rather than a negative - it adds to the realism, if anything. What I maybe would have said is tone down the overly colorful and playful clothing a couple of them are wearing - bright reds seem out of place with the tone of the trailer (on paper, bright red is blood, but in reality it's a bright colour that's out of place and should be darker), as does the Muppet shirt being worn by the running man.
Looks good though